State of the art in strength development of soil–cement columns

Abstract

The in situ deep mixing technique has been established as an effective means to effect columnar inclusions into soft clay to enhance bearing capacity and reduce settlement. In this paper, the factors governing strength development in soil–cement columns are presented. The clay-water/cement ratio, wc/C is the prime parameter for consideration in a laboratory mix design. The generalised strength equation is developed for various curing times and combinations of clay-water content, cement content and ash content. It helps minimise the number of trials required to arrive at the quantity of cement to be admixed. For low-strength soil–cement columns (laboratory 28 day strength less than 1500 kPa), the field strength, quf, made up from both dry and wet mixing methods is higher than 0·6 times the laboratory strength, qul. The quf/qul ratios for the wet mixing columns are generally higher than those for the dry mixing columns. This higher strength ratio is due to the dissipation of the excess water in the column (consolidation) caused by the field stress. A fast installation rate has been shown to provide high quality for low-strength columns.